Fuel cell stacks are electrochemical devices that produce water and an electric potential from a fuel, which typically is a proton source, and an oxidant. Many conventional fuel cell stacks utilize hydrogen gas as the proton source and oxygen, air, or oxygen-enriched air as the oxidant. Fuel cell stacks typically include many fuels cells that are fluidly and electrically coupled together between common end plates. Each fuel cell includes anode and cathode regions that are separated by an electrolytic membrane. Hydrogen gas is delivered to the anode region, and oxygen gas is delivered to the cathode region. Protons from the hydrogen gas are drawn through the electrolytic membrane to the anode region, where water is formed. Conventionally, the anode and cathode regions are periodically purged to remove water and accumulated gases in the regions. While protons may pass through the membranes, electrons cannot. Instead, the electrons that are liberated by the passing of the protons through the membranes travel through an external circuit to form an electric current.
A fuel cell stack is a group of fuel cells that are coupled together as a unit, typically between common end plates. The fuel cell stack receives flows of hydrogen and air from suitable sources and distributes these flows to the individual fuel cells in the stack. The fuel cell stack includes manifolds and other delivery conduits to deliver and remove fluids to and from the fuel cells within the fuel cell stack. Conventionally, a fuel cell stack includes current collectors that are adapted to be electrically connected to an external load so that power produced by the fuel cell stack may be used to satisfy the external load.
A factor that affects the performance, or efficiency, of a fuel cell stack to produce an electric current is the temperature of the stack. Accordingly, it is desirable to maintain the fuel cell stack within a range of suitable operating temperatures, such as within upper and lower threshold temperatures. During startup, the stack may not be at a temperature within this desired temperature range, and in such a situation, it is desirable to transition the stack to a temperature within this range. Accordingly, fuel cell systems typically include a temperature control system that is adapted to heat and/or cool the fuel cell stack, such as by delivering fluid streams into thermal communication with the stack to selectively heat or cool the stack.